Hepatitis C virus (HCV) is estimated to infect 170 million people worldwide [Purcell, R. H., Hepatitis C virus: historical perspective and current concepts. FEMS Microbiology Reviews, 1994. 14: p. 181-192.] Nearly four million individuals may be infected in the United States alone [M. J. Alter et al., “The Epidemiology of Viral Hepatitis in the United States, Gastroenterol. Clin. North Am., 23, pp. 437-455 (1994); M. J. Alter “Hepatitis C Virus Infection in the United States,” J. Hepatology, 31, (Suppl. 1), pp. 88-91 (1999)].
VX-950 is a competitive, reversible peptidomimetic hepatitis C virus (“HCV”) NS3/4A protease inhibitor with a steady state binding constant (ki*) of 3 nM (and with a Ki of 8 nM) [See International Publication No. 02/018369]:

In clinical trials, VX-950 has shown antiviral activity been shown to be an effective therapy against HCV, which is recognized as the causative agent for most cases of non-A, non-B hepatitis, with an estimated human sero-prevalence of 3% globally [A. Alberti et al., “Natural History of Hepatitis C,” J. Hepatology, 31., (Suppl. 1), pp. 17-24 (1999)].
However, because VX-950 is practically insoluble in water, formulating it to be suitable for administration is difficult.
Therefore, there is a need for a pharmaceutical composition that provides improved forms in a co-crystal that includes VX-950 and maintains adequate levels of VX-950 concentration in the environment of use.